This invention relates to a long stroke pumping apparatus and more particularly to long stroke pumping apparatus for oil wells in which a reversible capstan type central pumping unit is used.
Long stroke pumping apparatus has the advantage of slower pumping speed and therefore greater pumping efficiency in comparison with other types of pumping apparatus because the slow stroke provides adequate time for the pump to fill, thus promoting volumetric efficiency, eliminating gas lock and very considerably reducing shock, acceleration and harmonic loading.
Long stroke pumping apparatus using a variable contour capstan or winch type prime mover and a counterweight in a counterweight well to provide pump stroke turn around capability with a reduced input energy is broadly disclosed in U.S. Pat. No. 1,928,532 to Gillespie. The use of a grooved capstan with a counterweight in a well is also shown in U.S. Pat. No. 1,970,596 to Coberly. A further example of a variable diameter capstan or drum used with long stroke pumping apparatus is shown in U.S. Pat. No. 2,370,029 also to Gillespie and still further adaptations of the variable drum principle are disclosed in U.S. Pat. Nos. 3,285,091 and 3,528,305 to Kuhns et al and 3,695,117 to Ewing et al. The Kuhns et al arrangement in U.S. Pat. No. 3,285,081, for example, discloses the use of drums having central concentric portions and inner and outer decreased diameter eccentric portions over which well cables and counterweight cables operate during the turnaround portion of the pumping cycle. While each of the arrangements disclosed in these prior patents provides a reasonably effective long stroke pumping operation, such prior arrangements have not provided maximum attainable efficiency.